Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $171.80   13.257%   $194.5755   $194.58   $194.60   $194.60  
  Purchase #2 $34.84   13.839%   $39.6615   $39.66   $39.65   $39.70  
  Purchase #3 $56.37   5.871%   $59.6795   $59.68   $59.70   $59.70  
  Purchase #4 $15.30   8.705%   $16.6319   $16.63   $16.65   $16.60  
  Purchase #5 $168.63   9.871%   $185.2755   $185.28   $185.30   $185.30  
  Purchase #6 $35.57   3.399%   $36.779   $36.78   $36.80   $36.80  
  Purchase #7 $60.34   3.728%   $62.5895   $62.59   $62.60   $62.60  
  7 purchase totals = $542.85       $595.1924   $595.20   $595.30   $595.30